It is possible in a vehicle crash situation that the impact resulting from the crash could have a deleterious effect on any part of the vehicle door latch system, which is intended to keep the vehicle door latched to the vehicle body. However, in a crash, particularly in a roll-over situation where the door latch may be subjected to inertial forces directed over a wide angular range in three dimensions, the forces acting on the latch system may unintentionally actuate one or more latch system levers (which can be relatively long and have centers of mass located far from the rotation axis) and consecutively act to open the door latch. Needless to say, it is highly undesirable to have the vehicle door fling open in a crash situation, especially in a rollover.
It is known to prohibit the unintended movement of one or more release levers in a vehicle door latch due to inertial forces arising from a vehicle crash. See, for example, assignee's U.S. Publication No. 2006/0131892 by Pereverzev, which describes the use of an inertia lever actuated by a counterweight in a crash situation when the inertial forces exceed a threshold level. However, one of the limitations of that system is that the counterweight is actuated only by inertial forces acting along a relatively narrow angular range.
It is desirable to have a vehicular door latch system with a safety device that prohibits movement of a latch opening part when it moves that faster than a threshold speed indicative of a crash situation. In particular, it is desirable to prohibit such movement irrespective of the direction of inertial forces acting upon the latch system. And it is most desirable to have such a door latch safety system that operates in a crash situation, but not in a typical, daily encountered, door slam situation.